Spectroscopy of the E band of SO2 with a frequency-doubled single-mode dye laser

The rotational structure of the E band of SO₂ between 32720 and 32900 cm^?1 has been investigated by absorption spectroscopy with reduced Doppler width in a cooled cell at 190 K using a frequency-doubled cw single-mode dye laser. More than 400 lines in this band could be assigned, starting from a former partial analysis by Hamada and Merer. Severe perturbations in the upper state impede the assignment and prevent the unambiguous identification of many other lines in the spectrum. From the measured lines term values and molecular constants of the upper levels are derived. A comparison with spectra of very high resolution, taken in a collimated supersonic SO₂ beam demonstrates that the actual line density is by far higher than the spectral resolution in the cooled cell.